It is becoming an increasing trend in the automotive industry to centralise the hydraulic systems of some cars. Thus a car may have a single source of hydraulic fluid under pressure to operate the brakes, steering, suspension and other hydraulically operated functions. Under these circumstances it is the normal practice to employ a mineral oil hydraulic fluid. This is because these fluids have good lubricating properties such that wear in the various components of the system are kept to a minimum. Moreover seals are now available, and have been for some time, which are quite compatible with long chain hydrocarbons. However when hydraulic brake systems were first introduced the rubber seals, which were the only types of seal then available, were not compatible and tended to swell in the presence of mineral oil adversely affecting their proper function. It was found necessary therefore to employ a different fluid and the glycol, polyglycol, glycol-ether type fluids were developed. These products and their derivatives were, and are, quite satisfactory in most respects for use in simple brake systems but they do suffer from a lack of significant lubricating properties. Thus they are largely unsuitable for use as a central hydraulic system fluid. Nevertheless they have been in service for many years as a brake fluid and this has lead to the belief by unsuspecting members of the public that these fluids can be added to any brake or hydraulic system. Unfortunately this is not the case and by adding a non-hydrocarbon based fluid to a hydrocarbon based system the seals compatible with hydrocarbon fluids are attacked by and absorb the non-hydrocarbon fluid. The result is that the seal swells and again adversely affects its proper operation.
Despite prolific warnings on hydraulic fluid containers and hydraulic fluid reservoirs and in service manuals etc., it still occurs that Owners Or garage mechanics add non-hydrocarbon brake fluids to the mineral oil central hydraulic systems in their cars. With the system pump distributing the contamination to every part of the system all the seals become affected. By the time the owner notices anything wrong with the performance of his car one whole system must be dismantled, flushed out and new seals installed. This is a costly venture particularly if the owner of the vehicle notices the contamination by virtue of his brakes failing. It is mainly for this reason that vehicle manufacturers generally have not employed mineral oils as brake fluids, even though they are more suitable in many respects than conventional non-hydrocarbon brake fluids.
It is an object of this invention to alleviate this problem of contamination.